The invention relates to an apparatus for printing, coating or coloring webs by means of flat or cylindrical-stencil printing machines.
The printing, coloring or coating of webs by means of flat or cylindrical stencils requires devices with which the printing ink or the coating material is introduced uniformly over the entire stencil width and reaches the web through the perforations in the stencil.
Depending on the quality of the web material, the stencil must in this connection contact the web intimately or only slightly or be arranged at a distance from the web.
When cylindrical stencils are used, the peripheral velocity thereof must equal the velocity of the web during a printing operation, but the two velocities may differ during coloring or coating operations.
There are known a series of devices whose purpose is to achieve the above. In particular, there are employed slit and chamber squeegees.
Such slit and chamber squeegees consist basically of a hollow element provided with a slit and filled with ink or coating material. The open slit of these slit or chamber squeegees, which extends through the entire working width, contacts the stencil and must be sealed in relation thereto, so that no ink can escape and form an undesirable uncontrolled ink wedge in front of the chamber squeegee. Especially in chamber squeegees that are in the form of a tube and wherein (as described and illustrated in the French patent 1,116,729) liquid pressure is obtained by means of a communicating container, the sealing with sealing lips is a great problem already in the case of small working widths.
Besides, such a hollow element provided with a continuous longitudinal slit is extremely unstable and it is practically impossible to maintain the width of the slit constant without expensive components. Since with a certain quality of web material the amount of ink or coating material applied per unit of surface is a function of the width of the slit, the pressure of liquid in the ink chamber, the squeegee and the working speed, it is necessary to provide devices that take these problems into account.